The invention relates to systems and methods for ablating myocardial tissue for the treatment of cardiac conditions.
Physicians make use of catheters today in medical procedures to gain access into interior regions of the body to ablate targeted tissue areas. It is important for the physician to be able to precisely locate the catheter and control its emission of energy within the body during tissue ablation procedures.
For example, in electrophysiological therapy, ablation is used to treat cardiac rhythm disturbances.
During these procedures, a physician steers a catheter through a main vein or artery into the interior region of the heart that is to be treated. The physician places an ablating element carried on the catheter near the cardiac tissue that is to be ablated. The physician directs energy from the ablating element to ablate the tissue and form a lesion.
In electrophysiological therapy, there is a growing need for ablating elements capable of providing lesions in heart tissue having different geometries.
For example, it is believed the treatment of atrial fibrillation requires the formation of long, thin lesions of different curvilinear shapes in heart tissue. Such long, thin lesion patterns require the deployment within the heart of flexible ablating elements having multiple ablating regions. The formation of these lesions by ablation can provide the same therapeutic benefits that the complex suture patterns that the surgical maze procedure presently provides, but without invasive, open heart surgery.
As another example, it is believed that the treatment of atrial flutter and ventricular tachycardia requires the formation of relatively large and deep lesions patterns in heart tissue. Merely providing xe2x80x9cbiggerxe2x80x9d electrodes does not meet this need. Catheters carrying large electrodes are difficult to introduce into the heart and difficult to deploy in intimate contact with heart tissue. However, by distributing the larger ablating mass required for these electrodes among separate, multiple electrodes spaced apart along a flexible body, these difficulties can be overcome.
With larger and/or longer multiple electrode elements comes the demand for more precise control of the ablating process. The delivery of ablating energy must be governed to avoid incidences of tissue damage and coagulum formation. The delivery of ablating energy must also be carefully controlled to assure the formation of uniform and continuous lesions, without hot spots and gaps forming in the ablated tissue.
A principal objective of the invention is to provide improved systems and methodologies that control additive heating effects to form elongated straight or curvilinear lesion patterns in body tissue.
One aspect of the invention provides a device and associated method for creating elongated lesion patterns in body tissue. The device and method use a support element that contacts a tissue area. The support element carries at least two non-contiguous energy emitting zones, which are located in a mutually spaced apart relationship along the contacted tissue area. In use, the zones are conditioned to simultaneously emit energy to ablate tissue. The spacing between the zones along the contacted tissue area determines the characteristic of the elongated lesion patterns so formed.
When the zones are sufficiently spaced in close proximity to each other, the simultaneous transmission of energy from the zones in a unipolar mode (i.e., to an indifferent electrode) generates additive heating effects that create an elongated continuous lesion pattern in the contacted tissue area. When the zones are not sufficiently spaced close enough to each other, the simultaneous transmission of energy from the zones to an indifferent electrode do not generate additive heating effects. Instead, the simultaneous transmission of energy from the zones creates an elongated segmented, or interrupted, lesion pattern in the contacted tissue area.
In one embodiment, the spacing between the zones is equal to or less than about 3 times the smaller of the diameters of the first and second zones. In this arrangement, the simultaneous transmission of energy from the zones to an indifferent electrode creates an elongated continuous lesion pattern in the contacted tissue area due to additive heating effects. Conversely, in another embodiment where the spacing between the zones is greater than about 5 times the smaller of the diameters of the first and second zones, the simultaneous transmission of energy from the zones to an indifferent electrode does not generate additive heating effects. Instead, the simultaneous transmission of energy from the zones creates an elongated segmented, or interrupted, lesion pattern in the contacted tissue area.
In another embodiment, the spacing between the zones along the contacted tissue area is equal to or less than about 2 times the longest of the lengths of the first and second zones. This mutually close spacing creates, when the zones simultaneously transmit energy to an indifferent electrode, an elongated continuous lesion pattern in the contacted tissue area due to additive heating effects. Conversely, in another embodiment where the spacing between the zones along the contacted tissue area is greater than about 3 times the longest of the lengths of the first and second zones, when the zones simultaneously transmit energy to an indifferent electrode, an elongated segmented, or interrupted, lesion pattern results.
Another aspect of the invention provides a device and associated method for creating elongated curvilinear lesion patterns in body tissue. The device and method use a curved support element that contacts a tissue area. At least two non-contiguous energy emitting zones are carried on the curved support element mutually separated across the contacted tissue area.
In one embodiment, the zones are spaced across the contacted tissue area by a distance that is greater than about 8 times the smaller of the diameters of the first and second zones. In this arrangement, the simultaneously emission of energy forms an elongated lesion pattern forms in the tissue area that follows the curved periphery contacted by the support element, but does not span across the contacted tissue area. The curvilinear lesion pattern is continuous if the spacing between the zones along the support body is sufficient to create an additive heating effect. Otherwise, the curvilinear lesion pattern is segmented or interrupted along its length.
In another embodiment, the zones are positioned along the support body having a radius of curvature that is greater than about 4 times the smaller of the diameters of the first and second zones. In this arrangement, the simultaneous emission of energy by the zones forms an elongated lesion pattern in the tissue area that follows the curved periphery contacted by the support element, but does not span across the contacted tissue area. The curvilinear lesion pattern is continuous if the spacing between the zones along the support body is sufficient to create an additive heating effect. Otherwise, the curvilinear lesion pattern is segmented or interrupted along its length.